Our goal is to understand the control and role of inhibin in the ram. This Sertoli cell product apparently indirectly controls spermatogenesis by specifically suppressing follicle stimulating hormone (FSH) release from the anterior pituitary, but little is known about the interrelationship between inhibin, the gonadotropic hormones and androgens secreted by the testis. An understanding of the control of spermatogenesis requires an understanding of the interaction between testicular and gonadotropic hormones. An immunoassay prepared for porcine and ovine inhibin and our well established ram model now will make it possible to monitor inhibin levels. other Sertoli cell products, FSH, luteinizing hormone and testosterone (T) in serial samples of various biological fluids over long periods of time and to relate levels of these hormones to spermatogenic activity. To accomplish this we will: (1) Measure inhibin concentrations in rete testis fluid, testicular lymph, spermatic venous blood, peripheral blood, cauda epididymal fluid, and semen and determine how they are related to onset of spermatogenesis and season; (2) Determine factors that control inhibin secretion in the testis by exploiting the hemicastrated and "chemically" castrated ram models, by evaluating the effects of selective damage to the seminiferous eptithelium on the secretion of inhibin and other Sertoli cell proteins such as androgen binding protein and clusterin, and by studying the effects of FSH and T treatments on inhibin secretion in entire and "chemically" castrated rams; (3) Determine the biological effects of inhibin by administration of single doses of infusion of inhibin in intact and castrated rams and by measuring the effects of inhibin on cultured rat pituitary cells; and (4) Determine the effect of inhibin deprivation on gonadotropic hormone secretion and spermatogenesis using passive and active immunization.